The present disclosure relates generally to transducers, and particularly to transducer holders.
Ultrasonic transducers are used in measurement systems that employ an electrically actuated signal source, typically a piezoelectric crystal, mounted in a mounting assembly fixed to a housing or wedge, or fixed directly to a conduit, to propagate ultrasonic signals through a medium flowing in the conduit. In applications where the medium has a low density, such as a gaseous medium, or where the size of the conduit or the signal path length through the medium raises considerations of crosstalk, the amount of signal energy that can be received through the medium is relatively small. Furthermore, because the signal propagates through the gas with a velocity different from and generally slower than its propagation velocity through the solid structure of the conduit, it can be difficult to find a suitable timing window in which the received signal can be dependably distinguished from ringing or other energy propagated directly through the conduit walls.
To some extent the problem of signal strength may be addressed by appropriate impedance matching and the use of a large-area diaphragm to couple the crystal to the medium. However, accurate transducer alignment remains a key factor in signal strength reception, which is problematic for rigidly secured transducers that are out of alignment.
One of the largest and most costly problems to deal with in wetted ultrasonic flow metering is the question of transducer alignment. The problem typically arises during the manufacturing process of any wetted flow meter. Or, the problem may be rooted in the alignment of the mounting holes on the pipe (which are often far apart and on opposite sides of the pipe), the tolerances for each part in the holding mechanism, the tolerances in the transducers, and the crushing of gaskets used to retain the internal pipe pressures. When such alignment problems occur, the effects may be many and varied, effecting such things as turndown ratio, signal strength, jitter, and signal shape, for example. These effects may end up manifesting themselves as flow measurement inaccuracy, and may require many hours of work to correct. Other times, however, it may be determined that there is such a degree of misalignment that it is impossible to correct. Some solutions that have been considered in an attempt to address transducer misalignment include high precision machining of all parts involved, the use of quality control tools to reject a great quantity of out-of-alignment flowcells and other critical components, and redundant assembly checks, all of which being costly to implement.
Accordingly, there is a need in the art for an ultrasonic transducer holder that addresses problems associated with transducer misalignment.